confusion in "package and import "statement :(

[funkygarzon]

hi guys ,

I am in great confusion about the access specifier in package . please explain why public members alone can be accessed by the class in other package ? why not protect ? !!!!!

[JosAH]

hi guys ,

I am in great confusion about the access specifier in package . please explain why public members alone can be accessed by the class in other package ? why not protect ? !!!!!

As a matter of fact a class D can access the members in class B if those members are protected; class D has to extend class B. Protected access crosses package boundaries through extension.

kind regards,

Jos

[Hibernate]

Access/visibility modifiers (in order of rank [highest first]):

public — Accessible from everywhere
protected — Only accessible from the same package as well as from subclasses
* — Only accessible from the same package
private — Only accessible from the same class

* is the default access modifier and is used when no access modifier is used (i.e. in absence of the keywords: public, private, protected).
* is called ”default” or ”package private”.


Due to the existence of synthetic access (ugly enough to use; it is implicitly used) private methods/classes/&c can be access from inner classes,
otherwise at least package private must be used.

[funkygarzon]

As a matter of fact a class D can access the members in class B if those members are protected; class D has to extend class B. Protected access crosses package boundaries through extension.

kind regards,

Jos

Access/visibility modifiers (in order of rank [highest first]):

public — Accessible from everywhere
protected — Only accessible from the same package as well as from subclasses
* — Only accessible from the same package
private — Only accessible from the same class

* is the default access modifier and is used when no access modifier is used (i.e. in absence of the keywords: public, private, protected).
* is called ”default” or ”package private”.


Due to the existence of synthetic access (ugly enough to use; it is implicitly used) private methods/classes/&c can be access from inner classes,
otherwise at least package private must be used.

THANK YOU VERY MUCH FOR YOUR REPLY JosAH , Hibernate ,

Hope you are all fine by god grace .

Now coming to my doubt : practically i tried this theory by creating a class "Balance" in package called "MyPack" and i have created another class called "TestBalance" in another package called "MyPack2" but the protected members are not accessible by "TestBalance" ,so please help me and correct the error in my code below

package MyPack;

public class Balance {
	String name;
	double bal;
	protected  Balance(String n, double b) {
	name = n;
	bal = b;
	}
	protected  void show() {
	if(bal<0)
	System.out.print("--> ");

	System.out.println(name + ": $" + bal);
	}
	}

 package MyPack2;

import MyPack.*;
class TestBalance  {
	
	public static void main(String args[]) {
	/* Because Balance is public, you may use Balance
	class and call its constructor. */
	Balance test[] = new Balance[3];
	
	test[0] = new Balance("K. J. Fielding", 123.23);
	test[1] = new Balance("Will Tell", 157.02);
	test[2] = new Balance("Tom Jackson", -12.33);
	
	for(int i=0; i<3; i++) test[i].show();

	}
	
	}

[JosAH]

Class TestBalance doesn't extend class Balance so it doesn't have access to its protected members.

kind regards,

Jos

[funkygarzon]

Class TestBalance doesn't extend class Balance so it doesn't have access to its protected members.

kind regards,

Jos

Yes JosAH , i even tried like tried extending the Balance class , but still i am getting error bro :( . can you please correct my code ? please bro i am in great confusion

package MyPack;

public class Balance {
String name;
double bal;
protected Balance(String n, double b) {
name = n;
bal = b;
}
protected void show() {
if(bal<0)
System.out.print("--> ");

System.out.println(name + ": $" + bal);
}
}

package MyPack2;


class TestBalance extends Balance {

public static void main(String args[]) {

Balance test[] = new Balance[3];

test[0] = new Balance("K. J. Fielding", 123.23);
test[1] = new Balance("Will Tell", 157.02);
test[2] = new Balance("Tom Jackson", -12.33);

for(int i=0; i<3; i++) test[i].show();

}

}

[JosAH]

What is the exact error message? And where? For one thing: I don't see any protected data members (just methods).

kind regards,

Jos

[funkygarzon]

What is the exact error message? And where? For one thing: I don't see any protected data members (just methods).

kind regards,

Jos

ah yes bro , here only i am getting some confusion , ony protected members are allowed ? not protected methods ?

[JosAH]

ah yes bro , here only i am getting some confusion , ony protected members are allowed ? not protected methods ?

I didn't write that; show us your latest code and the exact compiler message you get.

kind regards,

Jos

[funkygarzon]

I didn't write that; show us your latest code and the exact compiler message you get.

kind regards,

Jos

java.lang.NoClassDefFoundError: Balance
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(Unknown Source)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknow n Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$000(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
Caused by: java.lang.ClassNotFoundException: Balance
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
... 12 more
Exception in thread "main"

the above one is the error message i am getting in Eclipse IDE bro

[abhilasha]

i think u missed the below statement
import MyPack.Balance;

in your TestBalance class

[abhilasha]

ur TestBalance class should lokk like this

package MyPack2;

import MyPack.Balance;

public class TestBalance extends Balance {

protected TestBalance(String n, double b) {
super(n, b);
}

public static void main(String args[]) {

TestBalance test[] = new TestBalance[3];
test[0] = new TestBalance("",123.25);
test[1] = new TestBalance("Will Tell", 157.02);
test[2] = new TestBalance("Tom Jackson", -12.33);

for(int i=0; i<3; i++) test[i].show();

}

}

[funkygarzon]

ur TestBalance class should lokk like this

package MyPack2;

import MyPack.Balance;

public class TestBalance extends Balance {

protected TestBalance(String n, double b) {
super(n, b);
}

public static void main(String args[]) {

TestBalance test[] = new TestBalance[3];
test[0] = new TestBalance("",123.25);
test[1] = new TestBalance("Will Tell", 157.02);
test[2] = new TestBalance("Tom Jackson", -12.33);

for(int i=0; i<3; i++) test[i].show();

}

}

Thanks for the reply bro , for the above code i am getting the below error bro ,

Exception in thread "main" java.lang.Error: Unresolved compilation problems:
The constructor Balance(String, double) is not visible
The constructor Balance(String, double) is not visible
The constructor Balance(String, double) is not visible
The method show() from the type Balance is not visible

at MyPack2.TestBalance.main(TestBalance.java:14)

[JosAH]

Thanks for the reply bro , for the above code i am getting the below error bro ,

Show us your code again because this is a mess; I suspect that you're still not extending from Balance in your TestBalance class; your compiler told you so but you still attempt to run the thing.

kind regards,

Jos

[abhilasha]

do u see m not calling new Balance(String,Double) from main method
instead u hv to use the sub Class ie new TestBalance(String,Double)

[JosAH]

do u see m not calling new Balance(String,Double) from main method
instead u hv to use the sub Class ie new TestBalance(String,Double)

That is not needed; please don't confuse the OP even more.

kind regards,

Jos

[funkygarzon]

Show us your code again because this is a mess; I suspect that you're still not extending from Balance in your TestBalance class; your compiler told you so but you still attempt to run the thing.

kind regards,

Jos

package MyPack;

public class Balance {
String name;
double bal;
protected Balance(String n, double b) {
name = n;
bal = b;
}
protected void show() {
if(bal<0)
System.out.print("--> ");

System.out.println(name + ": $" + bal);
}
}

package MyPack2;

import MyPack.Balance;
class TestBalance extends Balance {

protected TestBalance(String n, double b) {
super(n, b);
}
public static void main(String args[]) {

Balance test[] = new Balance[3];

test[0] = new Balance("K. J. Fielding", 123.23);
test[1] = new Balance("Will Tell", 157.02);
test[2] = new Balance("Tom Jackson", -12.33);

for(int i=0; i<3; i++) test[i].show();

}

}

do u see m not calling new Balance(String,Double) from main method
instead u hv to use the sub Class ie new TestBalance(String,Double)

yes bro , i can understand that you have created a contractor for "TestBalance" and calling super class contractor by using the keyword "super " , that is an amazing idea bro .... but still i am getting error , please check my above code :(

[Hibernate]

Do not construct, Balance, construct TestBalance:

Balance test[] = new Balance[3];

 test[0] = new TestBalance("K. J. Fielding", 123.23);
 test[1] = new TestBalance("Will Tell", 157.02);
 test[2] = new TestBalance("Tom Jackson", -12.33);

OR (if you decide you need to access new methods located in TestBalance, but not in Balance.)

TestBalance test[] = new TestBalance[3];

 test[0] = new TestBalance("K. J. Fielding", 123.23);
 test[1] = new TestBalance("Will Tell", 157.02);
 test[2] = new TestBalance("Tom Jackson", -12.33);

[Hibernate]

Because of show being protected only the second alternative will compile.


Edit:
Conclusion:
static members do never have access to protected members in other packages.

Edit 2:
Also:
protected constructors are only accessible by the line:
super(…);

[funkygarzon]

Because of show being protected only the second alternative will compile.


Edit:
Conclusion:
static members do never have access to protected members in other packages.

Edit 2:
Also:
protected constructors are only accessible by the line:
super(…);

wooooooow you are rocking bro , now all are working without error .

Because of show being protected only the second alternative will compile.

protected constructors are only accessible by the line:
super(…);

can you please explain me the above two sentence in detailed manner . ? thank s in advance bro ...